U.S. patent number 4,673,427 [Application Number 06/536,483] was granted by the patent office on 1987-06-16 for method of and device for drawing an optical fiber from a solid preform consisting substantially of sio.sub.2 and doped sio.sub.2.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Petrus J. Janssen, Aart A. Van Der Giessen, Victor A. Van Der Hulst.
United States Patent |
4,673,427 |
Van Der Giessen , et
al. |
June 16, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Method of and device for drawing an optical fiber from a solid
preform consisting substantially of SiO.sub.2 and doped
SiO.sub.2
Abstract
Optical fibres are drawn from a solid preform which consists
substantially of SiO.sub.2 and doped SiO.sub.2. After leaving the
heating zone, the fiber is guided through a space having a laminar
gas flow to restrict the temperature drop across the fiber so that
no extra stresses are incorporated in the fiber upon cooling. A
device for performing this method comprises a quartz pipe through
which the fiber is guided and in which a laminar gas flow is
maintained.
Inventors: |
Van Der Giessen; Aart A.
(Eindhoven, NL), Van Der Hulst; Victor A. (Eindhoven,
NL), Janssen; Petrus J. (Eindhoven, NL) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
|
Family
ID: |
19840370 |
Appl.
No.: |
06/536,483 |
Filed: |
September 28, 1983 |
Foreign Application Priority Data
Current U.S.
Class: |
65/424; 65/32.5;
65/435; 65/537 |
Current CPC
Class: |
C03B
37/027 (20130101); C03B 37/029 (20130101); C03B
2205/81 (20130101); C03B 2205/90 (20130101); C03B
2205/82 (20130101) |
Current International
Class: |
C03B
37/027 (20060101); C03B 37/029 (20060101); C03B
37/02 (20060101); C03B 037/027 () |
Field of
Search: |
;65/2,13,32,12,3.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
American Ceramic Society Bulletin, vol. 55 ,No. 2, pp. 195-197,
2/1976, Payne et al..
|
Primary Examiner: Lindsay; Robert
Attorney, Agent or Firm: Schechter; Marc D.
Claims
What is claimed is:
1. A method of drawing an optical fiber from a solid preform
comprising SiO.sub.2 and doped SiO.sub.2, said method comprising
the steps of:
heating an end of the preform to a temperature above 2000.degree.
C. in a furnace;
drawing an optical fiber from the heated end of the preform out of
the furnace; and
flowing a gas through the furnace to heat the gas to substantially
the temperature of the fiber at the end of the preform, and then
flowing the hot gas out of the furnace along the fiber at
substantially the same speed as the fiber is drawn from the
furnace, wherein the gas flow is laminar flow and the ggs flows
along the fiber for a selected time and distance chosen to assure
that the temperature gradient in the fiber is always less than that
at which stresses are produced which would increase the optical
attenuation of the fiber.
2. A method as claimed in claim 1, wherein each portion of the
fiber passes through the gas flow for at least 0.1 second.
3. A method as claimed in claim 2, wherein the gas does not attack
the furnace material.
4. A method as claimed in claim 2, wherein the gas is heated in the
furnace to a temperature within 200.degree. C. of the fiber
temperature.
5. A method as claimed in claim 1, wherein the gas is heated in the
furnace to a temperature within 200.degree. C. of the fiber
temperature.
6. A device for drawing an optical fiber from a solid preform
comprising SIO.sub.2 and doped SiO.sub.2, said device
comprising:
means for heating an end of the preform to a temperature at which
an optical fiber can be drawn from the preform;
means for drawing an optical fiber from the heated end of the
preform out of the heating means;
means for flowing a gas through the heating means to heat the gas
to substantially the temperature of the fiber at the end of the
preform, and then flowing the hot gas out of the heating means
along the fiber at substantially the same speed as the fiber is
drawn from the heating means, wherein the gas flow is laminar flow
and the gas flows along the fiber for a selected time and distance
chosen to assure that the temperature gradient in the fiber is
always less than that at which stresses are produced which would
increase the optical attenuation of the fiber.
7. A device as claimed in claim 6, wherein the means for flowing
the gas out of the furnace along the fiber comprises a quartz tube.
Description
BACKGROUND OF THE INVENTION
The invention relates to a method of and a device for drawing an
optical fiber from a silica or doped silica preform.
In drawing an optical fiber from a solid preform, the preform is
guided through a cylindrical furnace. The conical end of the
preform, from which the fiber is drawn, is heated at a temperature
above 2000.degree. C. The fiber is then guided through a device in
which a thin layer of a synthetic resin is provided on the fiber,
and is then guided through a furnace in which a solvent is removed
from the synthetic resin and/or the layer of synthetic resin is
polymerized.
It has been found that when the drawing speed is increased the
attenuation of an optical fiber and the bandwidth can increase.
It is presumed that the increase in attenuation is the result of
extra stresses which are present in a fiber and which are caused by
volume relaxation and structure orientation. These stresses occur
in particular if the temperature gradient traversed upon cooling
the fiber in the temperature range from 1200.degree. to
1800.degree. C. is particularly large (larger than 500.degree. C.
per sec.).
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of and a
device for drawing optical fiber which diminishes stresses in the
fibre such that when the drawing speed is increased the attenuation
in the fiber does not increase unacceptably.
According to the invention this object is achieved by a method in
which the optical fiber drawn from the conical end of the preform
is guided through a cooling space. In the cooling space, the drops
in temperature across the cross-section of the fiber at right
angles to the direction of drawing and in the direction of drawing
are smaller than the temperature drop at which glass stresses
increase the optical attenuation. In practice this can be
accomplished, for example, by producing a laminar gas flow of a
temperature not differing considerably from the fiber temperature
along the fiber at a speed at the surface of the fiber equal to or
slightly different from the fiber speed. In certain circumstances,
however, a turbulant gas flow may also be used, provided the gas
has a homogeneous temperature.
The temperature of the gas which comes in contact with the fiber
surface preferably differs less than 200.degree. C. from the fiber
temperature. The length and the cross-section of the space through
which the fiber is guided--which in a practical embodiment is
surrounded by a quartz tube--depends on the drawing rate and the
cooling effect of the gas flow in question through the space. It is
has been found that the desired effect is already achieved if the
fiber is in the space at least 0.1 second and there is a quiet
laminar gas flow.
In practice this means, for example, that at a drawing rate of
approximately 60 meters per minute, the length of the space is at
least 10 cm. At a drawing rate of 300 meters per minute, it is at
least 50 cm.
The gas which is led through the space may be, for example,
nitrogen, argon or oxygen, dependent on the furnace material. The
furnace material may not be attacked by the gas at the furnace
temperature during drawing. In the ideal case, the gas flow in the
space through which the fiber is guided, is determined
substantially by the speed at which the fiber is guided through the
space.
According to the invention a device for drawing an optical fiber
from a solid preform comprises a cylindrical drawing tube and an
inlet duct to lead a gas through the cylindrical heating space to
the tube. The fiber is guided through the tube after leaving the
cylindrical heating space.
BRIEF DESCRIPTION OF THE DRAWING
The sole drawing FIGURE is a schematic representation of the
optical fiber drawing device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preform 1 consisting of SiO.sub.2 and a core of doped SiO.sub.2,
for example GeO.sub.2 -doped SiO.sub.2, is guided a first
cylindrical space 2. A gas is led into space 2 by way of inlet duct
3. The gas flow can escape both upward and downward, but the
flanges 4 of the tubular body 5 surrounding the space 2 ensure that
the gas flows away substantially downward.
With preform 1, the gas flow reaches the actual drawing furnace
consisting of a cylindrical body 6 of conductive material, for
example graphite. The graphite is heated by means of an electrical
current (not further shown in the drawing). The preform is heated
in the furnace at 2100.degree. C., while the gas is also heated to
a high temperature as a result of thermal conductivity.
Via the duct 10 at the lower side of the cylindrical body 9, gas is
also led upward into the drawing furnace 6. In the embodiment shown
in the drawing the gas has a downward leakage current.
The gas with the fiber 7 then passes into the quartz tube 8. The
flow rate is controlled so that the gas has a laminar flow profile
in tube 8. At a drawing rate of 1 m/sec. the fibre temperature at
the outlet of the quartz tube 8 was: 1650.degree. C.
In a practical embodiment the gas blown in via the ducts 3 and 10
is argon.
A reduction of the attenuation by approximately 16% was realized by
means of the embodiment of the device described.
* * * * *